1. Field of the Invention
This invention relates to an active matrix type liquid crystal display device, specifically to an active matrix type liquid display device having a partial display function and an auxiliary capacitor line inversion drive function.
2. Description of the Related Art
In the active matrix type liquid crystal display device in which a pixel electrode of each pixel is provided with a video signal through a switching device such as a TFT (Thin Film Transistor), deterioration of a liquid crystal has been prevented by common electrode AC driving, that is, applying alternating electric potential to auxiliary capacitors and a common electrode that is facing the pixel electrodes.
However, capacitive load arising from the common electrode and all auxiliary capacitor lines and power consumption due to them remain large, since the common electrode AC driving in which the polarity of the video signal provided to each drain line is inverted once every horizontal period requires inverting the polarity of the electric potential at the common electrode and all the auxiliary capacitor lines once every horizontal period.
Japanese Patent Application Publication No. H12-81606 discloses a driving method to reduce power consumption of a horizontal drive circuit by inverting the polarity of the electric potential at the auxiliary capacitor lines at a constant interval while keeping the electric potential at the common electrode constant so as to reduce potential difference between the positive polarity and the negative polarity of the video signal in order to realize further low power consumption. The method is hereafter referred to as SC inversion driving which is a short form for an auxiliary capacitor line inversion driving method.
Japanese Patent Application Publication No. 2003-150127 discloses a dot inversion driving method in which voltages of different polarities are applied to pixel electrodes adjacent to each other in a direction of a gate line so that the pixels adjacent to each other in horizontal and vertical directions are applied voltages of different polarities as shown in FIG. 8, in order to prevent capacitive coupling caused in the SC inversion driving and resulting variations in a picture.
On the other hand, Japanese Patent Application Publication No. 2004-12890 discloses an active matrix type liquid crystal display device having a partial display function that performs a partial display at a time of power saving by providing pixels only in a partial display area selected from a liquid crystal display area with a desired video signal through the switching devices and providing pixels in the rest of the display area, that is defined as a background display area, with a white signal or a black signal through the switching devices.
This invention is directed to reduce the power consumption of the active matrix type liquid crystal display device using the SC inversion driving as described above when it performs the partial display function.